Atypical antipsychotic drugs block selective components of amphetamine-induced stereotypy

Evaluating outcomes of adult patients with acute lymphoblastic leukemia and lymphoblastic lymphoma treated on the GMALL 07/2003 protocol

Chemotherapy-based approaches still constitute an essential feature in the treatment paradigm of adult acute lymphoblastic leukemia (ALL). The German Multicenter Study Group (GMALL) is a well-established protocol for ALL. In this study, we assessed our recent experience with the GMALL 07/2003 protocol reviewing all adult ALL patients who were treated with GMALL in three major centers in Israel during 2007-2020. The analysis comprised 127 patients with a median age of 41 years (range 17-83). Sixty-two were B-ALL (49%), 20 (16%) patients were Philadelphia chromosome positive ALL, and 45 (35%) were T-ALL. The 2-year and 5-year overall survival rates were 71% and 57%, respectively. The 2-year relapse rate was 30% with 2-year and 5-year leukemia-free survival rates of 59% and 50%, respectively. Adolescents and young adults experienced significantly longer overall survival (84 months versus 51 months; p=0.047) as well as leukemia-free survival compared with older patients (66 months versus 54 months, p=0.003; hazard ratio=0.39, 95% confidence interval, 0.19-0.79; p=0.009). T-ALL patients had longer survival compared to B-ALL patients while survival was comparable among Philadelphia chromosome positive patients and Philadelphia chromosome negative patients. An increased number of cytogenetic clones at diagnosis were tightly associated with adverse prognosis (15-month survival for ≥2 clones versus 81 months for normal karyotype; p=0.003). Positive measurable residual disease studies following consolidation were predictive for increased risk of relapse (64% versus 22%; p=0.003) and shorter leukemia-free survival (11 months versus 42 months; p=0.0003). While GMALL is an effective adult regimen, a substantial patient segment still experiences relapse.

Challenging conventional models of psychiatric drug therapy: an alternative patient-centered approach

Modern psychopharmacology is based on the presumption that psychiatric drugs work by helping to correct an underlying abnormal brain state, or a chemical imbalance. For this article, i have termed this the disease-centered model of psychiatric drug action. Educational and advertising campaigns that have promoted this notion have resulted in soaring rates of use of drugs such as antidepressants and antipsychotics. However, drug action has not always been understood in these terms. This article challenges the disease-centered model of psychiatric drug action, and presents an alternative drug-centered view. The drug-centered model is based on the understanding that psychiatric drugs have psychoactive properties. They produce altered, drug-induced states in the individuals who take them, which may suppress the symptoms of mental disorders. Greater knowledge regarding the drug-induced effects of psychiatric drugs would help patients and prescribers to assess the pros and cons of drug treatment more accurately, and to use drugs more effectively. Further implications of this view are discussed.

Pharmacological profiles in rats of novel antipsychotics with combined dopamine D2/serotonin 5-HT1A activity: comparison with typical and atypical conventional antipsychotics

Combining antagonist/partial agonist activity at dopamine D2 and agonist activity at serotonin 5-HT1A receptors is one of the approaches that has recently been chosen to develop new generation antipsychotics, including bifeprunox, SSR181507 and SLV313. There have been, however, few comparative data on their pharmacological profiles. Here, we have directly compared a wide array of these novel dopamine D2/5-HT1A and conventional antipsychotics in rat models predictive of antipsychotic activity. Potency of antipsychotics to antagonize conditioned avoidance, methylphenidate-induced behaviour and D-amphetamine-induced hyperlocomotion correlated with their affinity at dopamine D2 receptors. Potency against ketamine-induced hyperlocomotion was independent of affinity at dopamine D2 or 5-HT1A receptors. Propensity to induce catalepsy, predictive of occurrence of extrapyramidal side effects, was inversely related to affinity at 5-HT1A receptors. As a result, preferential D2/5-HT1A antipsychotics displayed a large separation between doses producing 'antipsychotic-like' vs. cataleptogenic actions. These data support the contention that 5-HT1A receptor activation greatly reduces or prevents the cataleptogenic potential of novel antipsychotics. They also emphasize that interactions at 5-HT1A and D2 receptors, and the nature of effects (antagonism or partial agonism) at the latter has a profound influence on pharmacological activities, and is likely to affect therapeutic profiles.

Pharmacological evaluation of selected arylpiperazines with atypical antipsychotic potential

Six active compounds, among previously synthesized and screened arylpiperazines, were selected and evaluated for the binding affinity to rat dopamine, serotonin and alpha(1) receptors. Two compounds with benztriazole group had a 5-HT(2A)/D(2) binding ratio characteristic for atypical neuroleptics (>1, pK(i) values). Compound 2, 5-[2-[4-(2,3-dimethyl-phenyl)-piperazin-1-yl]ethyl]1H-benzotriazole, expressed clozapine-like in vitro binding profile at D(2), 5-HT(2A) and alpha 1 receptors and a higher affinity for 5-HT(1A) receptors than clozapine. Also, it exhibited the noncataleptic behavioural pattern of atypical antipsychotics and antagonized d-amphetamine-induced hyperlocomotion in rats.

Acute increases in monoamine release in the rat prefrontal cortex by the mGlu2/3 agonist LY379268 are similar in profile to risperidone, not locally mediated, and can be elicited in the presence of uptake blockade

Our recent work (Cartmell et al., Journal of Neurochemistry, 75 (2000) 1147-1154) demonstrated that systemic injection of the potent, selective mGlu2/3 receptor agonist, LY379268, acutely increased extracellular levels of dopamine, its metabolites DOPAC and HVA, and the 5-HT metabolite, 5-HIAA, in rat medial prefrontal cortex (mPFC). Here, we compared the acute effects of LY379268 with those of clozapine and risperidone (atypical antipsychotics) on extracellular levels of both dopamine and 5-HT in the mPFC of freely-moving rats. Uptake blockers were included to minimize metabolism of monoamines near the probe area. One hour after injection, LY379268 (10 mg/kg s.c.), clozapine (10 mg/kg s.c.) or risperidone (1 mg/kg s.c.) maximally increased dopamine by 224, 257 and 234% of basal levels. These effects were followed by maximal increases in DOPAC and HVA levels 2 to 3.5 hours after administration. LY379268, at 3 and 10 mg/kg s.c., and risperidone (1 mg/kg s.c.) also increased dialysate 5-HT to 169, 179 and 140% of basal levels and 5-HIAA to 144, 154 and 121% of basal levels, respectively. These neurochemical changes in the mPFC could not be mimicked when LY379268 (3 or 30 microM) was administered locally via the microdialysis probe. These data demonstrate that increases in extracellular monoamines in the rat prefrontal cortex evoked acutely by the mGlu2/3 agonist, LY379268, are similar in profile to risperidone, not locally mediated, and can be elicited in the presence of uptake blockade.

Effect of dopamine D2/D3 receptor antagonist sulpiride on amphetamine-induced changes in striatal extracellular dopamine

Amphetamine increases extracellular dopamine and induces locomotor and stereotypical behaviors in rats. This study examined the effect of the dopamine D2/D3 receptor antagonist sulpiride (50 mg/kg s.c.) on the dopaminergic response to amphetamine (0.5, 2.0, or 8.0 mg/kg i.p.) in male Sprague-Dawley rats. Extracellular dopamine in the striatum was monitored using in vivo microdialysis and high performance liquid chromatography with electrochemical detection. Dopamine concentration curves were analyzed using non-linear regression and residual F-testing. Amphetamine enhanced extracellular dopamine in a dose-dependent manner. Sulpiride augmented the increase in dopamine induced by 0.5 and 2 mg/kg amphetamine by decreasing the rate of dopamine concentration fall off in the extracellular space (P<0.05). Sulpiride also potentiated the amount of dopamine increased by 8 mg/kg amphetamine, but did so by affecting the maximum concentration achieved (P<0.05), not the onset or offset rates. We conclude that the primary effect of a dopamine D2/D3 receptor antagonist is a potentiation of the effect of amphetamine on extracellular striatal dopamine levels, which may contribute to the enhanced stereotypic effects observed when paired with amphetamine.

Cocaine-induced activation of striatal neurons during focused stereotypy in rats

As psychomotor stimulants, both amphetamine and cocaine elicit episodes of repetitive motor activation (focused stereotypy) known to involve the mesostriatal dopamine system. During amphetamine-induced focused stereotypy, motor-related neurons in the striatum respond with either an excitation or inhibition, depending on dose and behavioral pattern, whereas nonmotor-related units are inhibited. To assess striatal activity during the focused stereotypy induced by cocaine, both types of striatal units were recorded in ambulant rats. Either 20 or 40 mg/kg cocaine caused highly focused sniffing and head bobbing, which occurred in conjunction with activation of both motor- and nonmotor-related neurons. The activation of motor-related units was evident even when firing rate was compared during periods of matched pre- and post-drug behavior, arguing against movement as the sole basis for the drug-induced neuronal excitation. Subsequent administration of haloperidol (1.0 mg/kg) reversed but did not completely block the neuronal activation, while the behavioral response shifted away from focused stereotypy toward an increase in ambulation. Thus, the level of activation of both motor- and nonmotor-related striatal neurons may play a critical role in the behavioral response pattern induced by cocaine.

Neuroethological assessment of amphetamine-induced behavioral changes and their reversal by neuroleptics: focus on the amygdala and nucleus accumbens

1. An ethological approach was combined with intracerebral infusions of amphetamine to broaden understanding of how this drug acts on mesolimbic neuronal systems to alter behavior. 2. Rats, tested in sets of three, were allowed to interact with each other or with various novel objects in an open-field arena. Specific behavioral responses were assessed and grouped into several broad categories: motivation (movement directed toward novel objects), social (movement involving contact with other rats), and motor (movement without obvious direction toward environmental stimuli) as well as no movement (quiet rest). 3. Infusion of d-amphetamine (10 micrograms/microliter) into either the amygdala or nucleus accumbens elevated motor behavior relative to control rats in the set, but only amygdaloid infusions also increased the motivation score. Intra-amygdaloid clozapine or haloperidol blocked the increase in this score, but only clozapine also blocked the motor effects of intra-amygdaloid amphetamine. 4. Although neither neuroleptic in the accumbens blocked the amphetamine-induced increase in the motor category, both clozapine and haloperidol lowered the motivation score below the amphetamine level. 5. The results suggest a role for the amygdala in the motivational component of amphetamine-induced behavioral effects. Both neuroleptics, moreover, appear to reverse this component perhaps by acting via either amygdaloid or accumbal mechanisms. Although follow-up studies are warranted, a neuroethological approach is likely to shed new light on the neuronal systems underlying the complex behavioral changes induced by amphetamine and related stimulants.

Behavioral effects of clozapine and dopamine receptor subtypes

The atypical neuroleptic clozapine (CLZ) is an extremely effective antipsychotic that produces relatively few motoric side effects. However, CLZ displays limited antagonism at the dopamine (DA) D2 receptor, the receptor commonly thought to mediate the antipsychotic activity of neuroleptics. The mechanism of action behind the efficacy of CLZ remains to be determined. Miller, Wickens and Beninger [Progr. Neurobiol., 34, 143-184 (1990)] propose a "D1 hypothesis of antipsychotic action" that may explain the antipsychotic effects of CLZ. This hypothesis is built on the interactions between D2, cholinergic and D1 mechanisms in the striatum. These authors assert that although typical neuroleptics block D2 receptors, it is through an indirect action on D1 receptors that their antipsychotic action is manifest. The extra-pyramidal side effects produced by typical neuroleptics are hypothesized to be due to an indirect action on cholinergic receptors. It is argued that the anticholinergic properties of CLZ negate the D2 (motor side effects) action of CLZ, allowing CLZ to diminish psychotic symptoms through a direct action on D1 receptors. Thus, CLZ may function as a D1 receptor antagonist in behavioral paradigms. The current paper reviews and compares the behavioral profile of CLZ to those produced by D2- and D1-selective antagonists with specific reference to unconditioned and conditioned behaviors in order to more fully evaluate the "D1 hypothesis of CLZ action". Although the actions of CLZ remain unique, they do share some striking similarities with D1 receptor antagonists especially in tests of unconditioned behavior, possibly implicating the D1 receptor in the action of this antipsychotic drug.

Transient increases in catecholaminergic activity in medial prefrontal cortex and nucleus accumbens shell during novelty

Voltammetric recordings with electrochemically modified carbon-fiber electrodes were obtained from specific regions of the forebrain in rats given free-choice access to a novel environment. Entry into novelty increased the catechol signal in the medial prefrontal cortex and shell of the nucleus accumbens by more than 100%, but had no consistent effect in either the neostriatum or accumbal core. In both the medial prefrontal cortex and accumbal shell, moreover, the novelty-induced increase in catecholaminergic activity was detectable only during the initial entry into the novel compartment and did not reappear when animals returned to the familiar environment. These results support increasing evidence for a functional distinction between the accumbal core and shell, with the latter having been linked to brain reward mechanisms. The results also indicate that novelty activates, albeit very transiently, some of the same neurochemical systems believed to play a critical role in the reinforcing effects of certain drugs of abuse.

The characterization and outcome of stereotypical movements in nonautistic children

Stereotypies are patterned, repetitive, purposeless movements that are performed the same way each time. They are commonly seen in individuals with autism, schizophrenia, or mental retardation, and also occur as a feature of tardive dyskinesia and as movements in those with akathisia. We studied 10 children who had stereotypies but were not autistic or mentally retarded. Although most had an uneventful delivery, seven had mild to moderately delayed developmental milestones. Five had hyperactive behavior or attention-deficit problems. All appeared to be of normal intelligence. The median age of onset of stereotypies was 12 months. The stereotypies including arm flapping, arm and hand posturing, finger wiggling, body rocking, leg shaking, facial grimacing, involuntary noises, neck extension, and eye blinking. Of the 10 children, only two stopped having stereotypies eventually without medications.

Amygdaloid neurons respond to clozapine rather than haloperidol in behaving rats pretreated with intra-amygdaloid amphetamine

Single-unit activity was recorded from the amygdaloid complex in freely moving rats during an infusion of amphetamine directly into the recording site. Relative to the quiet resting period prior to the infusion, amphetamine routinely increased neuronal activity within 5-15 min after infusion onset, and this response continued for at least another 30 min. It was generally accompanied by marked increases in sniffing, rearing, locomotion, and grooming as well as by a tendency to turn to the ipsilateral side. Haloperidol and clozapine, typical and atypical antipsychotic drugs, respectively, were then tested in their ability to reverse these neuronal and behavioral effects. Both antipsychotics were administered subcutaneously at behaviorally effective doses within 10 min after termination of the amphetamine infusion. Haloperidol (1.0 mg/kg) failed to reverse the amphetamine-induced increase in amygdaloid neuronal activity and required more than 20 min to exert a partial blockade of the accompanying behavioral activation. Clozapine (10.0 mg/kg), in contrast, blocked the excitatory effects of amphetamine on all tested neurons and also blocked most amphetamine-induced behaviors within 10 min. Taken together, these results, which support other lines of electrophysiological evidence, point to the amygdala as a critical site in the differential behavioral effects of typical and atypical antipsychotic drugs.

Phencyclidine-induced increases in striatal neuron firing in behaving rats: reversal by haloperidol and clozapine

Amphetamine and related drugs of abuse facilitate dopamine transmission in the striatum. This action is believed to underlie the increase in firing of striatal motor-related neurons after amphetamine administration in behaving rats. The present study extended this electrophysiological investigation to phencyclidine (PCP), a nonamphetamine psychomotor stimulant that acts primarily as a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) glutamate receptors. Like amphetamine, PCP (1.0, 2.5, or 5.0 mg/kg) increased the activity of striatal motor-related neurons concomitant with behavioral activation. These effects were blocked by subsequent administration of either 1.0 mg/kg haloperidol or 20.0 mg/kg clozapine, typical and atypical neuroleptics, respectively. Dizocilpine (MK- 801), another noncompetitive NMDA antagonist, mimicked the effect of PCP. Collectively, these results indicate that amphetamine and NMDA antagonists exert comparable effects on striatal motor-related neurons, suggesting that the response of these cells to psychomotor stimulants is regulated by a dopaminergic-glutamatergic influence.

Amphetamine, cocaine, and dizocilpine enhance performance on a lever-release, conditioned avoidance response task in rats

A lever-release version of the conditioned avoidance response (CAR) task was used to assess the behavioral effects of several psychomotor stimulants in rats. The indirect dopamine agonists, d-amphetamine (0.1 and 0.25 mg/kg) and cocaine (7.5 and 15 mg/kg), enhanced performance on this task. Both drugs increased percent avoidance responses and decreased avoidance latency. A higher dose of amphetamine (0.5 mg/kg) also decreased avoidance latency but failed to improve percent avoidance. Similar effects were seen at low (0.01 and 0.025 mg/kg) and high (0.05 mg/kg) doses of dizocilpine (MK-801), a stimulant that acts as a noncompetitive antagonist of N-methyl-d-aspartate (NMDA) glutamate receptors. When combined with haloperidol (0.1 mg/kg), a dopamine antagonist, amphetamine (0.25 mg/kg) and dizocilpine (0.025 mg/kg) had differential effects on the lever-release CAR task. Thus, amphetamine-haloperidol was significantly better than haloperidol alone on percent avoidance but not on avoidance latency, whereas dizocilpine-haloperidol had the opposite effect: significantly better than haloperidol alone on avoidance latency but not on percent avoidance. Taken together, these results provide further support for dopaminergic mechanisms in CAR performance but suggest an opposing glutamatergic influence.

Ascorbic acid and atypical antipsychotic drugs: modulation of amineptine-induced behavior in mice

To provide a detailed characterization of individual kinds of behavior produced by ascorbic acid in combination with typical (haloperidol) or atypical (clozapine, sulpiride and remoxipride) antipsychotic drugs, the 'open-field' test was selected. Amineptine, an indirect dopamine agonist, was used as an explicit model of dopaminergic activity. Results showed that amineptine (5-10-20 mg/kg i.p.), dose-dependently, increased ambulation and rearing. Ascorbic acid (62.5-125-250 mg/kg i.p.) markedly inhibited the behavior of mice as well as the amineptine-induced hyperactivity. A combination of each typical or atypical antipsychotic drug (except clozapine 2.5 mg/kg i.p.) with amineptine (20 mg/kg i.p.) induced a significant increase in ambulation and rearing over that seen with the antipsychotic drugs alone. The combination of antipsychotic drugs with ascorbic acid 250 mg/kg i.p. led to a decrease in open-field parameters when compared with controls. In conclusion, these data provide further in vivo support for the effect of ascorbic acid on dopaminergic system and demonstrate that the antidopaminergic effects of both typical and atypical antipsychotic drugs may be enhanced with concurrent administration of ascorbic acid.

A vitamin as neuromodulator: ascorbate release into the extracellular fluid of the brain regulates dopaminergic and glutamatergic transmission

Ascorbate is an antioxidant vitamin that the brain accumulates from the blood supply and maintains at a relatively high concentration under widely varying conditions. Although neurons are known to use this vitamin in many different chemical and enzymatic reactions, only recently has sufficient evidence emerged to suggest a role for ascorbate in interneuronal communication. Ascorbate is released from glutamatergic neurons as part of the glutamate reuptake process, in which the high-affinity glutamate transporter exchanges ascorbate for glutamate. This heteroexchange process, which also may occur in glial cells, ensures a relatively high level of extracellular ascorbate in many forebrain regions. Ascorbate release is regulated, at least in part, by dopaminergic mechanisms, which appear to involve both the D1 and D2 family of dopamine receptors. Thus, amphetamine, GBR-12909, apomorphine, and the combined administration of D1 and D2 agonists all facilitate ascorbate release from glutamatergic terminals in the neostriatum, and this effect is blocked by dopamine receptor antagonists. Even though the neostriatum itself contains a high concentration of dopamine receptors, the critical site for dopamine-mediated ascorbate release in the neostriatum is the substantia nigra. Intranigral dopamine regulates the activity of nigrothalamic efferents, which in turn regulate thalamocortical fibers and eventually the glutamatergic corticoneostriatal pathway. In addition, neostriatonigral fibers project to nigrothalamic efferents, completing a complex multisynaptic loop that plays a major role in neostriatal ascorbate release. Although extracellular ascorbate appears to modulate the synaptic action of dopamine, the mechanisms underlying this effect are unclear. Evidence from receptor binding studies suggests that ascorbate alters dopamine receptors either as an allosteric inhibitor or as an inducer of iron-dependent lipid peroxidation. The applicability of these studies to dopamine receptor function, however, remains to be established in view of reports that ascorbate can protect against lipid peroxidation in vivo. Nevertheless, ample behavioral evidence supports an antidopaminergic action of ascorbate. Systemic, intraventricular, or intraneostriatal ascorbate administration, for example, attenuates the behavioral effects of amphetamine and potentiates the behavioral response to haloperidol. Some of these behavioral effects, however, may be dose-dependent in that treatment with relatively low doses of ascorbate has been reported to enhance dopamine-mediated behaviors. Ascorbate also appears to modulate glutamatergic transmission in the neostriatum. In fact, by facilitating glutamate release, ascorbate may indirectly oppose the action of dopamine, though the nature of the neostriatal dopaminergic-glutamatergic interaction is far from settled. Ascorbate also may alter the redox state of the NMDA glutamate receptor thus block NMDA-gated channel function.(ABSTRACT TRUNCATED AT 400 WORDS)

Cortical lesions attenuate the opposing effects of amphetamine and haloperidol on neostriatal neurons in freely moving rats

Neuronal activity was recorded from the neostriatum of freely moving rats at least 1 week following either sham or bilateral ablations of frontal and somatosensory cortex. In both groups of animals, the majority of neurons increased firing rate in close temporal association with spontaneous movement. No group differences emerged either with respect to baseline firing rates or open-field behavior. Following amphetamine administration, however, the excitatory response of motor-related neurons was suppressed in cortical-lesioned rats. A behavioral clamping procedure, which assessed neuronal activity during matched pre- and post-amphetamine behaviors, confirmed these results, suggesting that the amphetamine-induced changes in neuronal activity reflect a direct drug effect independent of behavioral feedback. In animals that received a subsequent injection of 1.0 mg/kg haloperidol, cortical lesions attenuated the ability of this neuroleptic to block both the behavioral and neuronal effects of amphetamine. Collectively, these results support mounting evidence for an important modulatory influence of cortical afferents on the amphetamine-induced excitation of neostriatal neurons and the reversal of this effect by haloperidol.

Influence of pharmacological manipulation of dopamine and opioid receptor subtypes on stereotyped behaviour of restricted-fed fowls

Effects on environmentally induced oral stereotypes (object pecking and drinker directed activity) of antagonists and agonists of dopamine and opioid receptor subtypes were examined in individually caged broiler breeder fowls subjected to chronic food restriction. Three drugs in each category were injected intravenously at three doses, and their effects compared with those of a saline control treatment. With dopamine antagonists, inhibition of both stereotypes was most marked with haloperidol (D2), intermediate with clozapine (D4), and lowest with SCH 23390 (D1). Increased sitting with the high doses of these three drugs may reflect sedation. With dopamine agonists, SKF 38393 (D1) suppressed both stereotypes slightly, quinpirole (D3) did so consistently and potently, possibly reflecting preferential presynaptic action, while bromocriptine (D2) inhibited drinker-directed activity consistently, but its initial suppression of object pecking changed to delayed stimulation with the high dose. This biphasic effect of bromocriptine may reflect change from pre- to postsynaptic action. Two of the opioid antagonists, naltrexone (mu) and MR 2266 (kappa, but also mu), inhibited object pecking partially, while naltrindole (delta) and the opioid agonists fentanyl (mu), BUBU (delta), and PD 117302 (kappa) had delayed and minor effects. These results suggest that expression of object pecking, but not necessarily drinker-directed activity, depends more on activation of D2 dopamine receptors than D1 receptors, the role of D3 and D4 receptors is less clear, and activation of mu and possibly kappa opioid receptors may play a contributory role.

Atypical antipsychotics, clozapine and sulpiride do not antagonise amphetamine-induced stereotyped locomotion

An automated tracking system which converted an animal's path between quadrants of a circular open field into a series of trips was used to analyse stereotyped locomotion in amphetamine treated rats. Amphetamine (3.5 mg/kg) increased the horizontal distance moved and the number and proportion of thigmotaxic trips around the perimeter of the apparatus (length 4 trips). To investigate the hypothesis that classic antipsychotics, but not atypical antipsychotics, would antagonise the repetitive boundary patrolling associated with amphetamine-induced hyperactivity, animals were pretreated with haloperidol (0.01, 0.025, 0.05, 0.075 mg/kg), clozapine (5, 10, 20 mg/kg) or (+/-)sulpiride (10, 20, 50 mg/kg) 30 min before 3.5 mg/kg amphetamine. The results showed that the classic antipsychotic haloperidol antagonised both hyperactivity and the increased proportion of length 4 trips. In marked contrast, the atypical antipsychotics clozapine and sulpiride antagonised hyperactivity but did not reduce the proportion of length 4 trips. The inability of atypical antipsychotics to reduce the repetitive boundary patrolling associated with amphetamine-induced hyperactivity is consistent with the action of these drugs on other forms of amphetamine-induced stereotyped behaviour, and indicates that locomotor routes under amphetamine are stereotyped. The measurement of trip lengths provides a sensitive tool for examining drug action on the spatial distribution of open field locomotion.

The involvement of D1 and D2 dopamine receptors in amphetamine-induced changes in striatal unit activity in behaving rats

Selective D1 (SCH-23390) and D2 (eticlopride and sulpiride) dopamine receptor antagonists were assessed for their ability to reverse the effects of 1.0 mg/kg D-amphetamine on excitatory motor-related neurons in the striatum of freely moving rats. SCH-23390 (0.125, 0.25, 0.5 and 1.0 mg/kg) rapidly and consistently blocked amphetamine-induced neuronal excitations as did eticlopride (0.25 and 1.0 mg/kg). In contrast, (-)-sulpiride (10, 20 and 40 mg/kg) failed to alter the neuronal response to amphetamine. Similarly, SCH-23390 and eticlopride also blocked the behavioral effects of amphetamine, but sulpiride did not. Collectively, these results support the involvement of D1 and D2 dopamine receptors in the excitatory effects of amphetamine on striatal neurons, but suggest caution in assessing the neuronal and behavioral effects of sulpiride.

Effects of four antipsychotics on punished responding in rats

In Experiment 1, the benzodiazepine chlordiazepoxide (CDP), two typical antipsychotics, haloperidol (HAL) and chlorpromazine (CPZ), and the atypical antipsychotic clozapine (CLZ) were evaluated for antipunishment effects in rats in a modified Geller-Seifter conflict procedure [MULT fixed interval (FI) 60-s, fixed ratio (FR) 1 (food + shock)]. In Experiment 2, CDP and thioridazine (THD) were similarly tested. CLZ (2.5 and 5.0 mg/kg), but not HAL, CPZ, or THD, selectively increased punished responding, although the magnitude of effect was smaller than that observed for CDP. Possible serotonergic mechanisms for CLZ's action in this model and the possible importance of serotonergic activity for the development of other atypical antipsychotic drugs are discussed.

Locomotor stereotypy is produced by methylphenidate and amfonelic acid and reduced by haloperidol but not clozapine or thioridazine

In addition to its well-known behavioral effects in rats, amphetamine also produces patterned locomotion (referred to below as locomotor stereotypy) in an open field. Locomotor stereotypy may be mediated by different mechanisms than those mediating the better-known behavioral effects of amphetamine. To determine whether the ability to produce locomotor stereotypy is an exclusive property of amphetamine or is a property of many amphetamine-like stimulants, several doses of methylphenidate and amfonelic acid were tested. The ability of both atypical and typical neuroleptics to block amphetamine-induced locomotor stereotypy was also tested. Both amfonelic acid and methylphenidate produced some degree of locomotor stereotypy. In addition, amphetamine-induced locomotor stereotypy was reduced by haloperidol but not by clozapine or thioridazine. These data suggest that locomotor stereotypy is more closely related to focused stereotypy than to hyperlocomotion.

Striatal single-unit responses to amphetamine and neuroleptics in freely moving rats

Single-unit recordings from 50 striatal neurons in freely moving rats revealed generally low activity (< 3 spikes/sec) during resting behavior and movement-related excitations in most (n = 36) neurons. While activating behavior, d-amphetamine (1.0 mg/kg, sc) usually excited and inhibited motor- and nonmotor-related neurons, respectively, relative to resting baseline firing rates. A behavioral clamping analysis, which controlled for neuronal effects secondary to behavior, yielded results suggesting a primary, amphetamine-induced excitation of striatal motor-related neurons. Haloperidol (0.1-1.0 mg/kg) strongly inhibited behavior and neuronal activity when injected 30 min after amphetamine. Clozapine (5.0-30.0 mg/kg) inhibited only selected behaviors, but reliably produced haloperidol-like reversals of amphetamine-induced neuronal excitations. A literature review revealed that the neuronal results in behaving animals differ markedly from the inhibitory striatal responses to amphetamine and the excitatory responses to dopamine antagonists often found in immobilized or anesthetized rat preparations. These contrasting, preparation-dependent results support a model based on drug interactions with a proposed neuromodulatory function of striatal dopamine, which is to facilitate or attenuate the activity of neurons receiving, respectively, substantial, or little excitatory afferent input.

BMY-14802, a sigma ligand and potential antipsychotic drug, reverses amphetamine-induced changes in neostriatal single-unit activity in freely moving rats

The effects of BMY-14802 (5, 10, or 20 mg/kg), a sigma-receptor ligand showing preclinical evidence of antipsychotic efficacy, were tested on single-unit activity in the neostriatum of freely moving rats with or without pretreatment with 1.0 mg/kg D-amphetamine. Relative to resting baseline, amphetamine activated the large majority of neurons that changed firing rate in close temporal association with movement. All doses of BMY-14802 reversed this neuronal response, but the effect was most pronounced at 20 mg/kg. This dose, however, was equally likely to reverse or to induce a haloperidol-like potentiation of those neurons inhibited by amphetamine. In contrast, 10 mg/kg BMY-14802 consistently reversed amphetamine-induced neuronal inhibitions. All doses of BMY-14802 attenuated the locomotor effects of amphetamine, but only the higher doses also blocked other aspects of the amphetamine behavioral response. By itself, BMY-14802 dose dependently inhibited motor-related neurons, but elicited less behavioral activation than amphetamine. BMY-14802 (20 mg/kg) also induced hindlimb ataxia and occasional backwards locomotion. Haloperidol (1.0 mg/kg) reliably suppressed both behavior and neuronal activity when injected 30 min after BMY-14802, whether or not amphetamine pretreatment was given. Thus, BMY-14802 shares with other neuroleptics the capacity to reverse amphetamine-induced excitations of neostriatal motor-related neurons, whereas other effects of BMY-14802 reveal some haloperidol-like actions at 20 mg/kg that do not occur at lower doses.

Dopamine-, NMDA- and sigma-receptor antagonists exert differential effects on basal and amphetamine-induced changes in neostriatal ascorbate and DOPAC in awake, behaving rats

Amphetamine and other dopamine agonists elevate the extracellular level of neostriatal ascorbate, which has been shown to modulate neuronal function. To assess the receptor mechanisms underlying neostriatal ascorbate release, drug-induced changes in both basal and amphetamine-induced ascorbate release were monitored voltammetrically in the neostriatum of freely moving rats. A variety of dopamine receptor antagonists decreased basal ascorbate and reversed the increase induced by 2.5 mg/kg D-amphetamine. Thus, compared to vehicle treatment, administration of classical (haloperidol) and atypical (clozapine) neuroleptics or selective D1 (SCH-23390) and D2 (sulpiride) antagonists completely reversed the amphetamine-induced rise in ascorbate and also lowered basal levels by 20-40%. These same effects occurred following injection of dizocilpine (MK-801), a non-competitive NMDA antagonist, whereas BMY-14802, a sigma ligand, reversed the amphetamine-induced rise without altering basal levels. Simultaneous measurements of extracellular DOPAC, a major dopamine metabolite, revealed that haloperidol, clozapine, sulpiride and BMY-14802 elevated basal levels and reversed the amphetamine-induced decline. Dizocilpine also increased basal DOPAC but failed to alter the DOPAC response to amphetamine, whereas both basal and amphetamine-induced changes in DOPAC were unaffected by SCH-23390. A combination of subthreshold doses of SCH-23390 and sulpiride, however, reversed both the amphetamine-induced release of ascorbate and the corresponding decline in DOPAC. Collectively, these results suggest that whereas dopamine, sigma, and NMDA receptors modulate neostriatal ascorbate release, they exert an opposing influence on extracellular DOPAC. All drugs attenuated at least some components of the amphetamine behavioral response, suggesting a role for multiple mechanisms in the behavioral effects of this drug.

A lever-release version of the conditioned avoidance response paradigm: Effects of haloperidol, clozapine, sulpiride, and BMY-14802

Rats trained on a lever-release version of the conditioned avoidance response (CAR) task were used to test the behavioral effects of established and putative antipsychotic drugs. Baseline CAR latencies decreased as the conditioned-unconditioned stimulus interval was shortened from 500 to 250 ms. Haloperidol, clozapine, and BMY-14802 decreased successful avoidance responses and increased avoidance latencies in a dose-dependent manner without affecting the latency of escape responses. In contrast, sulpiride failed to affect either successful avoidance response rates or avoidance latency. Sulpiride, however, significantly attenuated d-amphetamine-induced locomotion and rearing compared to vehicle-treated controls. Similar effects of these antipsychotics have been reported on shuttlebox avoidance, and these results now are confirmed in a CAR paradigm that achieves greater control over behavior. Because this paradigm elicits a discrete forelimb response without activating numerous muscle groups, it is potentially useful as a tool for examining neuronal mechanisms underlying the behavioral effects of antipsychotic drugs.

Muscarinic antagonists attenuate the increase in accumbens and striatum dopamine metabolism produced by clozapine but not by haloperidol

1. The effect of the muscarinic antagonists, scopolamine and atropine, were examined on the increase in extracellular 3,4-dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens and the striatum induced by haloperidol and clozapine by use of in vivo differential pulse voltammetry with carbon fibre electrodes in anaesthetized rats. 2. Animals received saline (1 ml kg-1, s.c.), scopolamine (1 mg kg-1, o.p.) or atropine (20 micrograms, i.c.v.) followed 15 min later by saline (10 microliters, i.c.v.), haloperidol (1 mg kg-1, s.c.) or clozapine (30 mg kg-1, i.p.) and extracellular DOPAC was simultaneously recorded in the nucleus accumbens and the striatum every 5 min for 60 min after drug administration. 3. Scopolamine or atropine alone had no effect on the DOPAC peak height but attenuated the increase in extracellular DOPAC induced by clozapine in both brain regions. Neither scopolamine nor atropine altered the haloperidol-induced increase in accumbens or striatal extracellular DOPAC. 4. The present results demonstrate that muscarinic antagonists attenuate the increase in accumbens and striatal dopamine metabolism in vivo produced by the atypical neuroleptic clozapine but not the haloperidol-induced increase in dopamine metabolism. The results indicate that central muscarinic receptors are involved in the actions on dopaminergic function of clozapine but not haloperidol.

Use of amfonelic acid to discriminate between classical and atypical neuroleptics and neurotensin: an in vivo voltammetric study

Previous ex vivo studies have shown that the non-amphetamine stimulant amfonelic acid potentiates the increase in DOPAC induced by classical but not by atypical neuroleptics. In the present study, we have demonstrated that this neurochemical model can be used to discriminate typical from atypical neuroleptics in vivo using differential pulse voltammetry with carbon fibre electrodes. The study also compared the effect of intracerebroventricular (i.c.v.) administration of neurotensin, on extracellular striatal DOPAC following amfonelic acid, with the effects of both classical and atypical neuroleptics. Saline or amfonelic acid (2.5 mg/kg s.c.) were administered; followed 5 min later by the classical neuroleptics haloperidol, perphenazine, or the atypical neuroleptics clozapine, thioridazine, or by neurotensin. After drug administration extracellular striatal DOPAC was recorded every 5 min for 90 min. Amfonelic acid did not alter basal striatal DOPAC but potentiated the increase in DOPAC induced by haloperidol (1.0 and 0.05 mg/kg s.c.) and perphenazine (10 mg/kg s.c.). Both clozapine (30 mg/kg i.p.) and thioridazine (20 mg/kg s.c.) increased extracellular DOPAC, but pretreatment with amfonelic acid prevented the increase in DOPAC produced by both drugs. Neurotensin (10 micrograms, i.c.v.), in a similar manner to the atypical neuroleptics, increased extracellular DOPAC in the striatum and the effect was prevented by amfonelic acid. The present study demonstrates that pretreatment with amfonelic acid is a valuable tool to discriminate between classical and atypical neuroleptics in vivo. The results also indicate that neurotensin in the presence of amfonelic acid has a profile similar to the atypical neuroleptics.

Effect of typical and atypical neuroleptics on the behavioural consequences of activation by muscimol of mesolimbic and nigro-striatal dopaminergic pathways in the rat

Direct injections of muscimol into the ventral tegmental area (VTA) or substantia nigra zona reticulata (SNR) have been used to selectively stimulate the mesolimbic and nigro-striatal dopamine pathways respectively. Such injections induced locomotor activity, rearing, sniffing and in some animals an intermittent grooming response. These responses were rapid in onset, dose-related and relatively short lasting (less than 40 min). Selective increases in dopamine turnover were seen in the nucleus accumbens and in the striatum following VTA and SNR injections of muscimol (100 ng) respectively. Haloperidol inhibited the behavioural consequences of VTA and SNR injections of muscimol with similar potency (ED50S 0.01-0.03 mg/kg IP), and fluphenazine did likewise (ED50S 0.05-0.16 mg/kg IP). However, thioridazine (ED50S VTA: 1.45-2.04 mg/kg IP, SNR 8.50-9.20 mg/kg IP) and in particular clozapine (ED50S VTA: 0.24-0.58 mg/kg IP, SNR: 6.10-9.70 mg/kg IP) were more potent at inhibiting the locomotor activity and sniffing responses due to VTA rather than SNR administered muscimol. Since dopamine D2 antagonists are believed to exert their anti-psychotic effects via an action on mesolimbic dopaminergic systems, and their ability to induce extrapyramidal side effects (EPS) is thought to be due to an action on nigro-striatal dopamine systems, these results suggest that the behavioural models described can be used to predict efficacy and side-effect liability of potential neuroleptic drugs.

Clozapine: an atypical neuroleptic

Since it was synthesized in 1960, much has been written about clozapine. Although a number of its properties are those of a neuroleptic, it displays marked differences from classical antipsychotics to the extent that it is currently listed as an atypical neuroleptic. A classical neuroleptic has been defined in man according to its antipsychotic properties, accompanied by extrapyramidal effects, and in animals according to its cataleptic properties, its ability to antagonize apomorphine and amphetamine stereotypies and to suppress the conditioned avoidance response. Moreover, the classical neuroleptic exerted depressive and anhedonic effects in most conditioning schedules. With clozapine, most of these properties are no longer strictly in force to the point that they call in question the validity of the tests carried out to detect the potential of neuroleptics. This article attempts to compare the characteristics of clozapine with those of classical neuroleptics from a toxicological, neuropharmacological, psychopharmacological and clinical point of view.

Intrastriatal infusions of ascorbate antagonize the behavioral response to amphetamine

Compared to saline, bilateral infusions of ascorbate (AA) into the neostriatum of freely moving rats attenuated rearing, head bobbing, and sniffing at various times after systemic amphetamine administration. Comparable AA infusions into overlying cerebral cortex failed to alter the amphetamine behavioral response. Intrastriatal AA also enhanced the ability of haloperidol to antagonize amphetamine-induced forepaw shuffling and locomotion. Voltammetric measurements in separate animals revealed a linear increase in neostriatal AA that remained within reasonable physiological limits over the course of the AA infusion. Thus, endogenous AA may modulate behavior via mechanisms intrinsic to the neostriatum.

The effects of haloperidol and amphetamine on ascorbic acid and uric acid in caudate and nucleus accumbens of rats as measured by voltammetry in vivo

The ability of haloperidol (0.1 mg/kg) to reduce the amphetamine-induced (2 and 5 mg/kg) increase in ascorbic and uric acid in anterior caudate and in nucleus accumbens was tested using voltammetry in vivo. In both areas, haloperidol reduced the amphetamine-induced increase in uric acid. In both areas, haloperidol only marginally affected the amphetamine-induced increase in ascorbic acid. Amphetamine-induced increases in uric acid were more nearly dose-related than changes in ascorbic acid. Of the two compounds, uric acid seems more likely to be associated with dopamine.